PHYSIOLOGY. 



761 



teeth in good condition, and these undergo de- 

 calcm'cation and softening. The process is not 

 a breaking down of the organic structure; for 

 if the material necessary to recalcify is provid- 

 ed in a form which Nature can appropriate, the 

 softening may be prevented ; and teeth which 

 have become softened may be rendered hard 

 and durable. Such repair has followed the re- 

 turn of residents natives of other places to their 

 old homes. This recalcifi cation is promoted by 

 the use of lime-water in the drink of subjects, 

 and more promptly and effectively by the use 

 of a new preparation of lime in the form of a 

 sirup, of much greater strength than aqua cal- 

 cis ; but the direct administration of the phos- 

 phates proved entirely unsatisfactory, and any 

 change from ordinary diet was found, as a rule, 

 entirely inadequate. 



J. N". Langley and J. S. Edkins have made 

 experiments to determine whether pepsin is 

 present to any considerable extent in the gas- 

 tric glands during life. Among the chief re- 

 sults of their investigation are that pepsin is 

 very rapidly destroyed by alkalies and by alka- 

 line salts. Proteids lessen the rate of destruc- 

 tion, probably by combining with the alkali or 

 alkaline salt. Pepsin prepared from a frog is 

 less rapidly destroyed than pepsin prepared 

 from a mammal. It having been found that 

 the aqueous extract of the gastric mucous mem- 

 brane of a hungry animal does not lose peptic 

 power, or loses very little, on brief treatment 

 with sodium carbonate 1 percent., the conclu- 

 sion was deduced that pepsinogen, but little or 

 no pepsin, is present in the gastric glands in 

 hunger. Thedifference between pepsinand pep- 

 sinogen in their behavior to reagents is one of 

 degree only and not one of kind. Pepsinogen 

 like pepsin is destroyed by alkalies and alka- 

 line salts, but the destruction is much slower, 

 Pepsinogen is very rapidly converted into pep- 

 sin by dilute mineral acids. In the absence of 

 acid, pepsinogen is fairly stable; in neutral and 

 in alkaline solutions its conversion is slow; and 

 in a glycerine extract it may remain unchanged 

 for years. Pepsinogen prepared from the frog 

 is not affected by passing a stream of oxygen 

 through it. In consequence of the rapid con- 

 version of pepsinogen to pepsin, it is difficult 

 to be certain whether pepsin is or is not pres- 

 ent in the gastric glands during digestion and 

 after the injection of peptone into the blood. 

 In both cases acid gastric juice is present in the 

 stomach, but it may have been found even after 

 death. In fact, pepsin is sometimes present in 

 an extract prepared from the gastric glands of 

 a digesting animal ; but it is not always pres- 

 ent, so that digestion does not necessarily cause 

 an accumulation of pepsin in the gland-cells. 

 It is concluded that normally the excretion of 

 pepsin from the gland-cells goes on hand in 

 hand with its formation from pepsinogen ; so 

 that neither in hunger, nor in digestion, nor 

 after the injection of peptogens into the blood, 

 is more than a trace of pepsin present. Car- 

 bonic acid destroys pepsinogen, and pepsin less 



readily ; while peptone delays the destruction, 

 and albumen and globulin in less degree. Some 

 of the experiments suggest the existence of dif- 

 ferent kinds of pepsin, either caused by the ac- 

 tion of reagents, or naturally formed from pep- 

 sinogen. 



Muscular System. Experiments to determine 

 the character of the muscular contractions 

 which are evoked by the excitation of the vari- 

 ous parts of the motor tract have been made 

 by Messrs. Horsly and Schafer, the results of 

 which they have supplemented with numerous 

 observations on voluntary and epileptoid con- 

 tractions in man. The principal conclusion 

 arrived at is that every prolonged contraction 

 of the skeletal muscles which is provoked by 

 excitation, whether natural or not, of any part 

 of the nerve- centers, is a tetanic contraction 

 that has been produced by a series of impulses 

 generated in the nerve -centers and passing 

 along the motor nerves at an average rate of 

 about ten per second. As to the place of gen- 

 eration of the rhythm it is certain that in some 

 cases it occurs in the lower nerve-centers (i. e., 

 in the motor nerve : cells of the spinal cord, 

 medulla oblongata, pons, and mesencephalon). 



Drs. S. Weir Mitchell and Morris J. Lewis 

 have published a paper on " Tendon-Jerk and 

 Muscle-Jerk in Disease," in which they hold 

 that the jerking of the knee is a direct muscu- 

 lar response, and not due to reflex action. 

 They also show that every muscular action, such 

 as winking, exaggerates the phenomena of the 

 jerkings. To demonstrate this, the patient 

 should lie down with the knee slightly bent, 

 and be directed to wink at the time the ten- 

 don is tapped, or just before, when it will be 

 noticed that the jerk is much increased. This 

 is more beautifully shown in the act of phona- 

 tion, when the patient should be directed to 

 count strongly, so as to bring the whole chest 

 into play at the time the test is applied. A 

 decided sensation, such as heat, cold, or an in- 

 jury, will increase the responsive power of the 

 muscle or tendon which has been struck. Both 

 the tendon and the muscle jerk are re-enforced 

 by irritation of distant parts, a phenomenon 

 which has been attributed to an increase of 

 tone in the muscle. This re- enforcement disap- 

 pears when the muscles are cut off from the 

 spinal centers. The experimenters noted also, 

 in associated movements, that in some cases, if 

 the patient is directed to shut his right hand, 

 the left hand will also shut to a certain extent; 

 and if he is sitting down, the leg may be drawn 

 up. Another symptom noticed is a certain de- 

 gree of prominence of the eyeballs. 



E. A. Schafer, from his investigation of the 

 rhythm of muscular response to volitional im- 

 pulses in man, deduces the conclusions that a 

 prolonged voluntary contraction is an incom- 

 plete tetanus produced by from eight to thir- 

 teen successive nervous impulses per second 1 . 

 About ten per second may be taken as the av- 

 erage. The average rate of muscular response 

 to volitional impulses is approximately the same 



